In an air-conditioning apparatus such as a multi-air-conditioning apparatus for a building, a refrigerant is circulated between an outdoor unit, which is a heat source unit disposed, for example, outside a building, and indoor units disposed in rooms in the building. The refrigerant transfers heat or removes heat to heat or cool air, thus heating or cooling a conditioned space through the heated or cooled air. Hydrofluorocarbon (HFC) refrigerants are often used as the refrigerant, for example. An air-conditioning apparatus using a natural refrigerant, such as carbon dioxide (CO2), has also been proposed.
Furthermore, in an air-conditioning apparatus called a chiller, cooling energy or heating energy is generated in a heat source unit disposed outside a structure. Water, antifreeze, or the like is heated or cooled by a heat exchanger disposed in an outdoor unit and it is carried to an indoor unit, such as a fan coil unit or a panel heater, to perform heating or cooling (refer to Patent Literature 1, for example).
Moreover, there is an air-conditioning apparatus called a heat recovery chiller that connects a heat source unit to each indoor unit with four water pipes arranged therebetween, supplies cooled and heated water or the like simultaneously, and allows the cooling and heating in the indoor units to be selected freely (refer to Patent Literature 2, for example).
In addition, there is an air-conditioning apparatus that disposes a heat exchanger for a primary refrigerant and a secondary refrigerant near each indoor unit in which the secondary refrigerant is carried to the indoor unit (refer to Patent Literature 3, for example).
Furthermore, there is an air-conditioning apparatus that connects an outdoor unit to each branch unit including a heat exchanger with two pipes in which a secondary refrigerant is carried to an indoor unit (refer to Patent Literature 4, for example).